Servomotor systems



y 5, 1964 R. HADEKEL 3,131,603

SERVOMOTOR SYSTEMS Filed Feb. 21, 1962 2 Sheets-Sheet 2 RUBEN HADEKELUnited States Patent Ofiice 3,131,603 Patented May 5, 1964 3,131,603SERVOMOTOR SYSTEMS Ruben Hadekel, London, England, assignor to TheSperry Gyroscope Company Limited, Brentford, England, a company of GreatBritain Filed Feb. 21, 1962, Ser. No. 174,803 Claims priority,application Great Britain Feb. 24, 1961 6 Claims. (Cl. 91-165) Thisinvention relates to servomotor systems and is particularly but notexclusively applicable to such systems for use in aircraft, for example,for moving a control surface. In such applications it is often desirableto make provision for alternative operational mode means, such as manualmeans, to perform the task of the servomotor-s in certain circumstances.The occurrence of a breakdown or fault in the servomotor system or in anautomatic pilot controlling the system are examples of suchcircumstances. In order to avoid interference with the operation of thealternative means by the servomotors it is often the practice to providea mechanical connection between the servomotors and the control surfaceor other load member which can be disconnected when the alternativemeans is in operation. One object of the present invention is to providea new and simple means of effectively disconnecting servomotors from aload member so as to make possible or facilitate the movement'of theload member by alternative means.

According to the invention, the improved servomotor system includes afixed frame, a pair of cooperating pressure jacks having axially spacedcylinders fixed mounted on the frame and respective oppositely arrangedpistons with effective and ineffective modes of operation, a load membermovably mounted on the frame between the pistons, .and alternative meansproviding the operational mode of the pistons. The range determiningmeans in the improved system includes mechanical means for connectingthe load member to the pistons in their effective mode of operationhaving a first part of fixed length between the load member and one ofthe pistons and a second part of a length equal to the length of thefirst part between the load member and the other of the pistons. Thealternative mode range determining means further includes means forbiasing the pistons in their ineffective mode of operation. The improvedsystem also includes change-over means operable to overcome the bias ofthe biasing means and provide a diiferential pressure input to thecylinders of the jacks to move the load member through the connectingmechanical means and pistons.

In one embodiment of the invention, the mechanical connecting means ofthe combination is a rocker pivoted on the load member with respectivefree arms of equal length whose ends operatively engage the respectivepis tons in their etfective mode of operation. Here, the biasing meansprovided are springs that are effective to separate the respectivepistons from engagement with the free ends of the rocker.

In another embodiment of the invention, the mechanical connecting meansis a flexible cable with parts of equal length between the load memberand the respective piston. Here, the included baising means are springsthat are elfective to release the tension in the cables connecting theload member and pistons. In order that the invention may be clearlyunderstood and readily carried into practice, a specific embodiment anda modification will now be described, by way of example, with referenceto the drawings accompanying the provisional specification, in which:

FIGURE 1 is a part-schematic, part cross-sectional view of a servomotorsystem conducted in accordance with the invention, and

FIGURE 2 is a part cross-sectional view of a modification of theembodiment shown in FIGURE 1.

Referring now to the arrangement shown in FIGURE 1, the improvedservomotor system there shown comprises a pair of hydraulic jacks,exemplified by the jack cylinders 1, 2 with their pistons 3, 4, whichhave hydraulic fluid applied to or exhausted from them through apertures7, 8. The pistons 3, 4 are carried on piston rod members 5, 6. Thecylinders 1, 2 of the jacks are fixed mounted on a frame 46 in axiallyspaced relation.

The differential fluid pressure input to the jacks moves the pistons 3,4 towards a pivoted load member 16 against the action of springs 9 and10 which are arranged to bias the pistons away from the load member. Themovable load member is mounted on a frame 46 between the pistons 3, 4.The load member 16 includes a mechanical connecting means consisting ofa rocker 11 with two arms or push rods 12, 13 of equal length which arereceived in recesses 14, 15 in the piston rod portions 6, 5respectively, the rocker being pivoted to the load member by means ofpivot 17. The load member 16 is pivoted to the frame 46 at 18 and itsmotion is transmitted to other members by way, for example, ofconnecting rods or cables 19. The pistons 3, 4 of the hydraulic jacksare arranged to be moved by hydraulic fluid applied to them under thecontrol of a common servo control valve 20. Between the servo controlvalve 20 and the jacks 1, 2 is an engaging valve 21, the purpose ofwhich is to allow hydraulic fluid in the jacks to escape to hydraulicfluid reservoir 34 when it is desired to move the load member 16 bymeans other than the jack pistons 3 and 4.

The engaging valve 21 comprises a cylinder 22 containing a piston memberhaving three lands 23, 24, 25 forming between them two annular chambers26, 27 which are movable along the cylinder to vary the hydraulic fluidpath to connect hydraulic lines 30, 31 leading to the jacks 2, 1,selectively to hydraulic lines 32, 33 leading to the hydraulic fluidreservoir 34 or hydraulic lines 28, 29 which are connected to servocontrol valve 20. The hydraulic fluid is drawn from this reservoir 34 bythe pump 35 from which it is fed to the servo control valve 20.

The piston member in the cylinder 22 is movable axially of the cylinderbetween two limits, and is biassed towards one of these limits, namelythe right-hand one as shown in the drawing, by means of a spring 36. Atthis limit the lines 30, 31 are connected to the lines 32, 33 throughthe annular chambers 27, 26 respectively. In normal operation theengaging valve 21 is held against the bias of spring 36 by means of thesolenoid 37, so that the lines 28, 30 are connected together throughannular chamber 27 and the lines 29, 31 are connected together throughannular chamber 26. The solenoid 37 may be controlled either manually orautomatically, thus, means may be provided for automaticallyde-energising the solenoid in the event of a fault occurring in thehydraulic system. In a modification, the piston member in the cylinder22 is arranged to be moved hydraulically instead of electromagnetically,for example by applying hydraulic fluid under pressure from the pump 35to the right-hand end face of the land 25.

The servo control valve 20 receives hydraulic fluid under pressure frompump 35 and, according to the position of its valve member 20a, variesthe output pressure in lines 28 and 29 differentially between a value alittle less than the output pressure from pump 35 and a value much lessthan the pump output pressure but sufficient, if applied to one of thejacks, to move the piston through its full range of movement inopposition to the force of spring 9 or spring 10 alone. Thus when theengaging Valve 21 is held against the bias of spring 36 by energisationof the solenoid 37, and the lines 28, 3t) and 23, 31 are connected byway of the annular chambers 27 and 26, these pressures reach the jacks2, 1. The pressures are, in normal operation, always sufficient tomaintain the piston rod portions 6 and in operative engagement with theends of the rocker arms 12 and 13 of the connecting means determiningthe eifective mode of operation of the pistons. Motion of the loadmember 16 occurs through the connecting mechanical means and pistonsbrought about by the suitable positioning of the valve member 20a ofvalve 20 and its resulting difierential pressure output.

Here when the valve 21 is operated to bring rocker 11 under the controlof the hydraulic system, the piston rod members 6 and 5 may not engagethe arms 12 and 13 simultaneously. To avoid or minimise jolting orerroneous movement of the load member in the interval which elapsesbefore both piston rod members are engaged by the corresponding arms, apick-off device is provided having one part 38 fixedly mounted on rocker11, and another part 39 fixed to an arm 47 which is movable with respectto part 38 and urged by suitable resilient means 33a into a yieldablycentered condition with respect to part 38. Part 39 carries tworesilient feeler members 40 and 41 which are so positioned as to beengaged by the piston rod members just before the latter are in fullengagement with arms 12 and 13 of the rocker 11.

A comparatively strong output signal from this pickoff device is appliedto input terminals of an amplifier 42 the output signal of which isarranged to control the servo control valve 20. Other input terminals ofthe amplifier 42 have applied to them a position demand signal from aposition setting device 43 and a position feedback signal from a furtherpick-off device 43a associated with the load member 16.

During the process of bringing the load member under the control of thehydraulic system, the output signal from the pick-01f device 38, 39 isadded to the other two signal inputs to the amplifier 42. If, forexample, the piston rod portion 5 is in advance of the piston portionrod 6 as they are being brought into engagement with the ends of thearms 13 and 12 of rocker 11 the resilient arm 41 will be contacted bythe piston rod portion 5 and part 39 of the pick-off device will bemoved from its position of symmetry to produce a bias signal in such asense that the pressure in jack 1 is reduced and that in jack 2increased. This will result in a speeding up of the advance of piston 4,and a reduction in any force exerted by piston 3 upon the load member.In this way the piston rod portions 5 and 6 are brought into engagementwith the load member 16 without appreciably disturbing it. A switch(39a) is provided for cutting out the signal from the pick off when fullengagement is attained. To prevent such erroneous operation of thesystem during the interval before the cut out switch is operated asmight be caused by a lack of symmetry in the pick-off arrangement, thepick-off may be provided with a dead spot at the centre of its range.This can be readily provided in an E-type pick-01f by very slightlyincreasing the length of the armature member 39 in relation to thelength of the E-shaped core member 38.

Part of an alternative arrangement is shown in FIG- URE 2 of thedrawings. Here the load member 16 is also pivoted at 18 on the frame 46and the piston rod portions 5, 6 are connected to it through flexiblemembers, such for example as the cables 45, 44. Application to thejacks, 1, 2 of hydraulic fluid under pressure through the lines 31, 30moves the pistons 3, 4, and with them the piston rod portions 5, 6, awayfrom the member 16 against the bias of the springs 9, 10. This movementserves to tension the cables 45, 44 and so transmit the forces acting onthe pistons 3, 4 to the member 16. When the pressure of the hydraulicfluid applied to the jacks through the lines 30, 31 falls below thevalue required to overcome the bias of the springs 10, 9, the pistonsand their associated piston rod portions are moved towards the arm 16,so slackening the cables 44, 45 and allowing movement of said member 16independently of the servomotor system. It will be appreciated that thedistance between the ends of the piston rod portions 5, 6 when fullyextended from the jacks 1, 2 under the bias of springs 3, 10 is suchthat sufiicient room is left to enable the member 16 to be moved overthe desired range. Here, the cables 44, 45 provide connecting parts ofequal lengths between the load member 16 and the respective pistons thatare included in the alternative mechanical connecting means of thesystem for determining the effective and ineffective modes of operationof the pistons.

While a hydraulic arrangement has been described by way of example, theinvention could equally well be applied to a pneumatic arrangement.

What is claimed is:

1. A servomotor system of the character described including a fixedframe, a pair of cooperating pressure jacks having axially spacedcylinders fixedly mounted on the frame and respective oppositelyarranged pistons with effective and ineffective modes of operation, aload member movably mounted on the frame between the pistons;alternative means providing the operational mode of the pistonsincluding mechanical means for connecting the load member to the pistonsin their efiective mode of operation having a first part of fixed lengthbetween the member and one of the pistons and a second part of a lengthequal to the length of the first part between the member and the otherof the pistons, and means for biasing the pistons in their ineffectivemode of operation; and changeover means operable to overcome the bias ofthe biasing means and provide a difierential pressure input to thecylinders of the jacks to move the member through the connectingmechanical means and pistons.

2. A system as claimed in claim 1, in which the load member is pivotallymounted on the frame, and the mechanical connecting means is a rockerpivoted on the member with respective free arms of equal length whoseends operatively engage the respective pistons in their eifective modeof operation.

3. A system as claimed in claim 1, in which the load member is pivotallymounted on the frame, and the mechanical connecting means is a flexiblecable with parts of equal length between the load member and therespective pistons.

4. A system as claimed in claim 2, including an arm movably mounted onthe load member having feelers arranged to engage the respectivepistons, means for yieldably centering the arm with respect to the loadmember, and a pick-off providing an input to the system having a partfixed to the arm and a part fixed to the rocker.

5. A system as claimed in claim 2, in which said pis ton biasing meansare springs effective to separate the respective pistons from engagementwith the free ends of the rocker.

6. A system as claimed in claim 3, in which said piston biasing meansare springs effective to release the tension in the cable connecting theload member and pistons.

References Cited in the file of this patent UNITED STATES PATENTS2,380,510 Fitch July 21, 1945 2,400,233 Hicks May 14, 1946 2,630,785 RayMar. 10, 1953 2,987,048 Buxton et a1 June 6, 1961

1. A SERVOMOTOR SYSTEM OF THE CHARACTER DESCRIBED INCLUDING A FIXEDFRAME, A PAIR OF COOPERATING PRESSURE JACKS HAVING AXIALLY SPACEDCYLINDERS FIXEDLY MOUNTED ON THE FRAME AND RESPECTIVE OPPOSITELYARRANGED PISTONS WITH EFFECTIVE AND INEFFECTIVE MODES OF OPERATION, ALOAD MEMBER MOVABLY MOUNTED ON THE FRAME BETWEEN THE PISTONS;ALTERNATIVE MEANS PROVIDING THE OPERATIONAL MODE OF THE PISTONSINCLUDING MECHANICAL MEANS FOR CONNECTING THE LOAD MEMBER TO THE PISTONSIN THEIR EFFECTIVE MODE OF OPERATION HAVING A FIRST PART OF FIXED LENGTHBETWEEN THE MEMBER AND ONE OF THE PISTONS AND A SECOND PART OF A LENGTHEQUAL TO THE LENGTH OF THE FIRST PART BETWEEN THE MEMBER AND THE OTHEROF THE PISTONS, AND MEANS FOR BIASING THE PISTONS IN THEIR INEFFECTIVEMODE OF OPERATION; AND CHANGEOVER MEANS OPERABLE TO OVERCOME THE BIAS OFTHE BIASING MEANS AND PROVIDE A DIFFERENTIAL PRESSURE INPUT TO THECYLINDERS OF THE JACKS TO MOVE THE MEMBER THROUGH THE CONNECTINGMECHANICAL MEANS AND PISTONS.